The present invention relates to a display panel including a plurality of semiconductor crystals in each of which are created at least two regions of opposite conductivity types forming an electroluminescent junction, the crystals being situated at the bottoms of cavities reflecting the light emitted by said crystals. The cavities, created in strips of a given length, are disposed either in lines or in columns, or in a combination of lines and columns according to a previously chosen configuration and each of them comprises at least two metallic contact pads made respectively to contact the two regions of the semiconductor crystal situated at the bottom.
Electroluminescent elements are often used in groups in a disposition established in x-y coordinates.
In the greater part of the applications known so far, said electroluminescent elements, generally semiconductor diodes, which thus form a matrix, must be disposed in a larger quantity on a reduced surface and the emission of the radiations of each of them must moreover be localized in a substantially punctiform zone, their luminous intensity being then concentrated by means of a suitable optical system.
One of the possible applications of such an assembly relates to automobile traffic control. For example, the assembly may be employed in traffic lights or motor car lighting such as cross-roads traffic lights or rear lights or blinkers of motor cars. Such an application requires taking into account the dimensions imposed upon said lights, and an effort must be made relating to the ratio: EQU number of crystals/unit of surface area
so as to reduce the cost of the assembly.
French Patent Application No. 82 05 189 describes an assembly of a plurality of electroluminscent diodes bearing on a suitable support and a light conductor formed by a centered reflector system constituted by an optical element and a reflector of the same optical axis.
The optical system in said light conductor comprises a plate having parallel faces in the central part of which a thin convergent element having spherical diopters is included, and the reflector is constituted by a concave mirror having a double quadratic associated with a flat mirror perpendicular to the optical axis and formed by the support of the diodes.
However, from the point of view of optical efficiency the assembly described in said Patent Application does not provide the anticipated results.
From the optical point of view, for example, experience shows actually that the plate having parallel faces and the converging element satisfy a very precise requirement of directivity of the light beam and that any choice of directivity differing even slightly will necessitate a new optical system. This drawback makes the light conductor burdensome in practice.
Further, despite the low current consumption of the electroluminscent elements, there accumulation on the insulating support supporting them leads to thermal problems which also have effects on the luminous efficiency. The power dissipated by 50 diodes may be estimated, for example, 4 W and transformed into calories: said calories which flow through the support with difficulty produce a rise in temperature of the assembly which leads to a reduction of the luminous efficiency in a ratio which may reach 0.7 % per .degree. C.
Said rise in temperature may also produce degradations of the greater part of the materials generally constituting the reflector.
Actually, if the latter is constituted by a plastics material covered by a paint, then by a metallic film deposited by a method of metallization in a vacuum, and by another protecting paint, said film then presents adhesion defects and the paints themselves may blister or be cracked.
As regards the insulating support carrying the light conductor(s), it is constituted by a so-called "printed" circuit because it supports a network of connections necessary for the electrical connections of the electroluminescent elements together and to the exterior.